AN EXPERIMENTAL-STUDY OF THE MECHANICAL RESPONSE OF FROZEN BIOLOGICALTISSUES AT CRYOGENIC TEMPERATURES

An experimental study of the mechanical response of frozen soft biolog ical tissues to applied compressive stresses is presented. This study is related to the mechanical stresses that develop due to the contract ion of frozen tissues in cryopreservation as well as in cryosurgical p rocedures. The main concept in this study is that the stresses associa ted with the constrained contraction of the frozen tissue. i.e., due t o temperature variations within the frozen tissue, can be simulated by an external mechanical load which is applied to the frozen tissue whi le the tissue is maintained at a uniform temperature A new apparatus f or measuring compressive stresses and strains of frozen biological tis sues in cryogenic temperature range is presented. A new technique for processing the fresh biological tissue into a cylindrical frozen sampl e for mechanical testing is introduced. Results of compression tests o n rabbit liver, kidney. and brain are presented and are compared with available data from the literature on sea ice and single ice crystals. An unusual response of frozen biological tissues to compressive stres s was observed: after the initial. roughly linear elastic portion ther e was a series of sudden stress drops at constant strain, each followe d by a linear increase oi. stress with strain to the next drop. This p henomenon, which is attributed to the accumulation of microcracks, bro adly resembles plastic deformation, and thus provides some support for simple mechanical models invoked in theoretical studies. (C) 1996 Aca demic Press, Inc.